Curated prerequisite DAGs over educational concepts are used in this paper as a graph-RAG test bed rather than a target application. Their value is that the directed acyclic graph (DAG) of prerequisite relations is explicit, inspectable, and auditable, which makes graph expansion policies easy to specify and to ablate. The aim is to test whether graph-aware retrieval helps beyond a matched dense baseline, not to argue that graph retrieval dominates general RAG settings. Consequently, conclusions drawn on these DAGs are scoped to curated, template-based prerequisite QA.